The subject matter of this invention is related to fuse devices for conducting high values of rated current while providing a current limiting capability during a fusing operation. The subject matter of this invention relates specifically to the utilization of current limiting fuse devices in combination with expulsion type fuse devices for accomplishing the above result.
It is known that current limiting fuses provide effective current limiting operation when connected in series circuit relationship with a load and source. It is also known that expulsion type fuses when connected in series circuit relationship with a load and source generally do not have significant current limiting capability at high values of rated current but rather provide high voltage isolation after fusing and relatively low impedance to high values of rated load current. On the other hand, current limiting fuses provide relatively high impedance to high values of normal rated load current. A current limiting fuse is disclosed in U.S. Pat. No. 3,740,687, issued June 19, 1973 to F. L. Cameron. An expulsion fuse is disclosed in U.S. Pat. No. 3,401,245, issued Sept. 10, 1968 to F. L. Cameron. Both of the above patents are assigned to the assignee of the present invention. It would be advantageous if an electrical fuse device could be provided for utilization in circuit relationship with a source and load to provide the best features of an expulsion fuse, i.e., high voltage isolation after fusing and relatively low impedance during the conduction of high values of normal rated load current and the best features of a current limiting fuse, i.e., current limitation during a fusing operation for high values of fault current.